Transcript No Slide Title

2. Suspension Systems - 1
Theory Support
Automotive – Steering & Suspension
Suspension Systems - 1
Topics covered in this presentation:
 Basic Suspension System
 Spring Types
 Suspension System Construction
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2. Suspension Systems - 1
Theory Support
Automotive – Steering & Suspension
Basic Suspension System
The primary purpose of a suspension system is to support the weight of the
vehicle and give a smooth ride.
It is desirable that it should also:
 allow rapid cornering without body roll when the car leans to one side.
 keep tires in firm contact with the road at all times and conditions.
 prevent body squat (tilting down at rear) when accelerating.
 prevent body dive (tilting down at front) when braking.
 allow front wheels to turn for steering.
 keep the wheels vertical and in correct alignment at all times.
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2. Suspension Systems - 1
Theory Support
Automotive – Steering & Suspension
Elementary Suspension System
In a modern car, the typical
suspension components are:
Coil spring
Shock absorber
A control arm that pivots
on the vehicle frame.
The steering knuckle
is ball-jointed to the
control arm to allow for
vertical and horizontal
movements.
Steering
knuckle
Control arm
This simple example
has a coil spring and
built-in shock absorber.
Frame
All of the components are
attached to the frame.
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2. Suspension Systems - 1
Theory Support
Automotive – Steering & Suspension
Independent Suspension
A solid axle tilts with road bumps.
Solid axle
This causes both wheels to be tilted.
Independent suspension allows
one wheel to move up or down
without appreciably affecting
the other.
Independent Suspension
The design of the control arm
keeps the wheel upright.
This is the preferred system for
most modern cars.
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2. Suspension Systems - 1
Theory Support
Automotive – Steering & Suspension
Coil Spring
There are four main types of springs in common use:




Coil Spring
Leaf Spring
Torsion Bar
Air Spring
Coil spring
Coil Spring
This consists of a spring-steel
rod wound into a coil.
It is ideally suited to
independent suspension.
This is the most common type of
spring used by modern vehicles.
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2. Suspension Systems - 1
Theory Support
Automotive – Steering & Suspension
Leaf Spring
Flat plates of spring steel
are bolted together.
The front end of the spring is
bolted directly to the frame.
A swinging shackle at the rear
permits the length of the spring
to change when it is flexed.
U-bolts and plates clamp
spring to axle housing.
This type used to be common but
is now only used on a few rear
suspension systems.
Swinging shackle
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2. Suspension Systems - 1
Theory Support
Automotive – Steering & Suspension
Torsion Bar
One end of the torsion bar is fixed to the vehicle frame.
The other end of the torsion bar is attached to the control arm so that it
twists as the control arm moves up or down.
A strut bar prevents front or rear movements of the control arm.
When the control arm is moved by the suspension,
the twisting motion of the torsion bar
resists the movement.
Torsion bar Vehicle frame
Control arm
Strut bar
Steering knuckle connects
onto control arm
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2. Suspension Systems - 1
Theory Support
Automotive – Steering & Suspension
Air Spring
This is normally a two-ply rubber cylinder filled with compressed air.
It has similar rebound reaction
to a coil spring.
The air spring is much
lighter in weight,
compared with its
steel sprung
equivalent, resulting in
increased economy
and an adjustable
controllable ride.
Rebound (expansion) allows the control arm to move down when there
are hollows in the road surface.
This is especially adaptable to automatic leveling systems.
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2. Suspension Systems - 1
Theory Support
Automotive – Steering & Suspension
Control Arm
A control arm holds the steering knuckle,
bearing support or axle housing.
Bushings
The control arm is connected to the
steering knuckle by a ball joint.
Ball joint
Control arm bushings
act as bearings.
The control arm is
free to move up
and down with the
suspension.
Control arm
Steering knuckle
Rear suspension control arms may have bushings at both ends.
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2. Suspension Systems - 1
Theory Support
Automotive – Steering & Suspension
Control Arm and Strut Rod
The picture below shows a typical independent
suspension front wheel unit.
Steering knuckle
Frame
The control arm is attached to
a frame or cradle.
The other end of the control
arm is attached to the
steering knuckle.
A strut rod prevents forward
or backward movement of the
control arm.
Rubber bushes on both the control
arm and the strut rod soften the action
and absorb shocks.
Control arm
Strut rod
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2. Suspension Systems - 1
Theory Support
Automotive – Steering & Suspension
Ball Joints
Ball joint is short for ball-andsocket joint.
Steering knuckle
Upper pivot
ball joint
Ball joints allow limited
movement in all directions.
Two pivots, one above
and one below, keep the
wheel vertical.
Drive axle
A front wheel system is shown,
including a steering knuckle.
The drive axle must allow
universal movement.
Hub
Lower pivot
ball joint
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2. Suspension Systems - 1
Theory Support
Automotive – Steering & Suspension
Shock Absorber
Top mount
The function of a shock absorber is to
reduce spring oscillations (up and down
movements) following a road shock.
The upper end (top mount) is attached to
the frame and the lower end (bottom
mount) to the suspension unit.
A piston and valve assembly
moves in an oil-filled cylinder.
Movement is controlled by the
valve, rate-of-flow, restriction.
A pressurized gas chamber is
sometimes added to prevent air
bubbles in the oil causing foaming.
The cylinder is enclosed in a dust cover.
Dust
cover
Oil cylinder
Piston and
valve
assembly
Pressurized
gas chamber
Bottom
mount
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2. Suspension Systems - 1
Theory Support
Automotive – Steering & Suspension
MacPherson Strut Shock Absorber
This is a combined coil spring and shock
absorber assembly.
The upper pivot is the strut
mounting to the frame.
A ball bearing mounting at the top
allows steering movements.
Bump stops or rebound bumpers
prevent metal-to-metal contact.
The shock absorber is inside the strut.
The lower spring seat is part of
the shock absorber body.
Metal strut tube houses shock absorber
reservoir, valve, pressure tube etc.
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2. Suspension Systems - 1
Theory Support
Automotive – Steering & Suspension
Stabilizer (Sway) Bar
The purpose of the stabilizer bar is to prevent excessive body leaning
when turning.
Links both the lower
control arms together.
When one end of the bar
is deflected in either
direction (up or down), the
bar tries to pull the other
side in the same direction,
this has the effect of
stabilizing and controlling Stabilizer bar
the suspension.
When cornering, the outside of the body tends to drop, which twists the bar
and limits the amount of the sway.
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2. Suspension Systems - 1
Theory Support
Automotive – Steering & Suspension
Track (Lateral Control) Bar
A track bar prevents side-toside rear axle movement
when cornering.
Support bracket
Diagonal brace
Track bar
One end of the track bar
is fastened to the axle,
the other end to the
frame on the opposite
side of car.
Rear (solid) axle
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